debug: add generic boot write-range tracing

[mstan]

Summary

Extracts the remaining useful Crash Bash diagnostic from #13 / NyperYuhgard's
b07cb79251ecdca85aca94ba5dbfd731b67e10a7 without taking the title-specific
hard-code or the unrelated stale branch:

• adds PSX_WTRACE_BOOT=lo,hi[;lo,hi...] for caller-selected, half-open RAM
  ranges armed before guest execution;
• feeds those ranges into the existing boot-pinned write trace, retaining
  address/value/width, PC, RA, registers, frame, and DMA attribution;
• accepts physical or KSEG addresses and supports multiple ranges;
• adds focused parser coverage, TCP documentation, and source provenance.

The companion generic misaligned-dispatch diagnostics from the source commit
were already extracted in #28.

Co-authored with and credited to @NyperYuhgard.

Crash Bash assessment

The original report is mechanically plausible, but its specific corrupt-value
diagnosis is not independently reproduced.

With a verified local retail Greatest Hits build and
PSX_WTRACE_BOOT=0x000B3A80,0x000B3B00, the watched range is genuinely active.
At physical 0x000B3AC4, however, the observed nonzero write was the loaded
MIPS instruction 0x8C65B690, from guest PC 0x80048FA8 at frame 395; not the
reported 0x6766BD35 pointer. That supports preserving the diagnostic as a
generic tool, but not encoding the address or interpretation in the runtime.

Validation

• Recompiler/unit suite: 38/38 passed.
• Crash Bash: drove Load Game to its no-save warning, then New Game through
  character select, the hub, and live Crashball gameplay. Survived two
  deterministic fuzz phases (540 input pulses, frame 24594), with audio
  active, zero unsupported mid-block executions, and zero unknown dispatch
  tails.
• Core-four matched baseline/candidate regression:
  • Tomba (db2302c): title, memory-card slot chooser, village gameplay, and
    deterministic fuzz passed.
  • Tomba 2 (fa6a75d): title, load-slot chooser, seaside gameplay, and
    deterministic fuzz passed.
  • Mega Man X6 (83e2ee0): full memory-card read path and intro-stage
    gameplay passed; deterministic fuzz plus extended input skipping reached
    live combat.
  • Ape Escape (564a86e): Load Game, full memory-card read path, opening
    sequence/gameplay, and deterministic fuzz passed.
• Every final core-four report exited through TCP quit with 0 unsupported
  mid-block executions and 0 unknown dispatch tails. All matched runs held
  normal 16.683 ms frame pacing and active audio. Mega Man X6 and Ape Escape
  each completed 72/72 card reads with no aborts.

The previously noted default SDL3/MinGW failure is resolved in this PR.
SDL_main.h is SDL3's single-header entry-point implementation and was being
included through the shared compatibility header, emitting one WinMain from
every SDL-using translation unit. It now has one owner in main.cpp, protected
by a source-invariant test. A clean fetched-SDL 3.4.10 MinGW build linked and
smoke-ran Crash Bash through SDL3/OpenGL to frame 1374 with normal 16.683 ms
pacing and a clean report.

Validated and ready to merge.